http://hdl.handle.net/2027.42/58625 2013-06-20T00:06:42Z http://hdl.handle.net/2027.42/94188 A Comparative Study of Coherent & Incoherent Doppler Lidar Techniques Skinner, Wilbert R.; Hays, Paul B. Our purpose in this report is two-fold: 1) describe the basics of the coherent and incoherent systems, particularly the latter, and 2) compare the performance of the two technologies in a meaningful way. We conclude that an incoherent system, if properly designed, can achieve accuracies that are comparable to those obtained by a coherent system. An incoherent system can make useful wind measurements even when the aerosol concentration is very low. This insures that global wind measurements can be made. An incoherent system has no problems with speckle, and the measurements can be readily averaged to reduce the total wind uncertainty (measurement error plus atmospheric wind variance). These factors need to be considered very carefully when considering the relative merits of the two technologies. 1994-06-03T00:00:00Z http://hdl.handle.net/2027.42/64202 A miniature sensor for electrical field measurements in dusty planetary atmospheres Renno, Nilton O.; Kok, J. F.; Kirkham, H.; Rogacki, S. "Dusty phenomena such as regular wind-blown dust, dust storms, and dust devils are the most important, currently active, geological processes on Mars. Electric fields larger than 100 kV/m have been measured in terrestrial dusty phenomena. Theoretical calculations predict that, close to the surface, the bulk electric fields in martian dusty phenomena reach the breakdown value of the isolating properties of thin martian air of about a few 10 kV/m. The fact that martian dusty phenomena are electrically active has important implications for dust lifting and atmospheric chemistry. Electric field sensors are usually grounded and distort the electric fields in their vicinity. Grounded sensors also produce large errors when subject to ion currents or impacts from clouds of charged particles. Moreover, they are incapable of providing information about the direction of the electric field, an important quantity. Finally, typical sensors with more than 10 cm of diameter are not capable of measuring electric fields at distances as small as a few cm from the surface. Measurements this close to the surface are necessary for studies of the effects of electric fields on dust lifting. To overcome these shortcomings, we developed the miniature electric-field sensor described in this article." 2008-01-01T00:00:00Z http://hdl.handle.net/2027.42/64195 The effects of electric forces on dust lifting: Preliminary studies with a numerical model Kok, J. F.; Renno, Nilton O. "Atmospheric dust aerosols affect the Earth's climate by scattering and absorbing radiation and by modifying cloud properties. Recent experiments have indicated that electric fields produced in dusty phenomena such as dust storms and dust devils could enhance the emission of dust aerosols. However, the generation of electric fields in dusty phenomena is poorly understood. To address this problem, we present results from the first physically-based numerical model of electric fields in dust lifting. Our model calculates the motion and collisions of air-borne particles, as well as the charge transfer during these collisions. This allows us to simulate the formation of electric fields as a function of physical parameters, such as wind stress and soil properties. Preliminary model results show that electric fields can indeed enhance the lifting of soil particles. Moreover, they suggest that strong electric fields could trigger a positive feedback because increases in the concentration of charged particles strengthen the original electric field, which in turn lifts additional surface particles. We plan to further test and calibrate our model with experimental data." 2008-01-01T00:00:00Z http://hdl.handle.net/2027.42/64192 The theory of interaction between wave and basic flow Ling-Kun, Ran; Boyd, John P. "This paper investigates the interaction between transient wave and non-stationary and non-conservative basic flow. An interaction equation is derived from the zonally symmetric and non-hydrostatic primitive equations in Cartesian coordinates by using the Momentum-Casimir method. In the derivation, it is assumed that the transient disturbances satisfy the linear perturbation equations and the basic states are non-conservative and slowly vary in time and space. The diabatic heating composed of basic-state heating and perturbation heating is also introduced. Since the theory of wave-flow interaction is constructed in non-hydrostatic and ageostrophic dynamical framework, it is applicable to diagnosing the interaction between the meso-scale convective system in front and the background flow. It follows from the local interaction equation that the local tendency of pseudomomentum wave-activity density depends on the combination of the perturbation flux divergence second-order in disturbance amplitude, the local change of basic-state pseudomomentum density, the basic-state flux divergence and the forcing effect of diabatic heating. Furthermore, the tendency of pseudomomentum wave-activity density is opposite to that of basic-state pseudomomentum density. The globally integrated basic-state pseudomomentum equation and wave-activity equation reveal that the global development of basic-state pseudomomentum is only dominated by the basic-state diabatic heating while it is the forcing effect of total diabatic heating from which the global evolution of pseudomomentum wave activity results. Therefore, the interaction between the transient wave and the non-stationary and non-conservative basic flow is realized in virtue of the basic-state diabatic heating." 2008-01-01T00:00:00Z